Merge pull request #430 from happypeter/timeline

<main> doesn't work in some broswer, and clearfix rocks
Merge pull request #431 from happypeter/timeline

correct single course timeline style
add statistical info
Add statistical info for single course
adjust indent
update gem font-awesome-rails

  gem list -r font-awesome-rails # get the latest version
use new font-awesome icon
change timeline icons
correct the number of authors on timeline page
i